As shown in FIG. 2, a conventional indoor unit 101 of an air conditioner, in many cases, comprises a front grille 103 having a window 132 for ventilation in front of a heat exchanger 105, and further in front of the front grille 103, a front panel 104 having a suction grille (composed of a plurality of louvers 141) formed in its central portion 104a and an unshown upper portion. A front grille lower portion 103b and a front panel lower portion 104b are both flat-shaped and overlaid on each other. The front grille 103 is mounted integrally to a unit casing 102 while the front panel 104 is openable and closable to the unit casing 102. During cooling operation, a low-temperature refrigerant is made to flow through a heat exchanger tube 151 of the heat exchanger 105 of this indoor unit 101. In this state, with an air fan 106 driven into rotation, indoor air is sucked in through gaps 142 of the suction grille of the front panel 104 and the window 132 of the front grille 103, and air cooled through the heat exchanger 105 is blown out into a room 199 through an air outlet 108 located below the front panel 104.
A diffuser 109 having an inverted L-shaped cross section is provided at a position on a front panel 104 side within the air outlet 108, more specifically, between the front grille lower portion 103b and a drain pan front portion 107a. This diffuser 109, a horizontal portion 109b of which forms an upper wall of the air outlet 108, works to change kinetic energy fed to the blown-off air into pressure. Meanwhile, a generally flat-shaped guide vane 110 for changing the angle of the blown-off air is provided at a lower portion within the air outlet 108.
During the cooling operation, indoor air being higher in temperature and containing more moisture than the blown-off air makes contact with the front face side of the front panel lower portion 104b. As a result, in such an indoor unit 101 as described above, the front grille lower portion 103b and the front panel lower portion 104b are cooled by the blown-off air during the cooling operation, causing a problem that dew condensations 180 occur to the front face side of the front panel lower portion 104b. Particularly when the diffuser 109 is provided at a position on the front panel 104 side within the air outlet 108, the rear face side of the front panel lower portion 104b is cooled relatively strongly, making the dew condensations 180 more likely to occur to the front face side of the front panel lower portion 104b. Therefore, it has been conventional practice to apply a heat insulating material 112 on the rear face side of the front grille lower portion 103b overlaid on the front panel lower portion 104b in order to prevent the front panel lower portion 104b from being cooled from the rear face side by the blown-off air.
Also, the diffuser 109 has a temperature near the temperature of the blown-off air because the horizontal portion 109b is cooled by the blown-off air flowing through the air outlet 108. Therefore, high-temperature indoor air (indicated by the broken-line arrow in FIG. 2) that has entered to around a vertical portion 109a of the diffuser 109 is cooled, causing dew condensations to occur to the diffuser 109. Thus, as a conventional practice, heat insulating materials 113, 114 and unwoven cloth 15 are applied to the rear face of the vertical portion 109a, the lower face of the horizontal portion 109b and the upper face of the holizontal portion 109b, respectively, in the diffuser 109 so as to prevent involvement of warm air and thereby prevent dew condensations, while a heat insulating material 111 is applied also on the front face side of the drain pan front portion 107a facing the diffuser 109.
Like this, in the conventional indoor unit 101, a number of heat insulating materials or the like are used as measures for dew condensations in the vicinity of the front panel lower portion. This causes a cost increase, as a problem.